1. Field of the Invention
The present invention relates to generating a regulated voltage, and more particularly, to a novel voltage regulator (e.g., an LDO regulator) which maintains excellent output voltage stability with a capacitor-free structure.
2. Description of the Prior Art
Linear regulators are used in modern electronic systems for providing efficient power-management capability. One of the most commonly used linear regulators is a low dropout regulator.
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a conventional low dropout regulator 100. The conventional low dropout regulator 100 includes an error amplifier 110, a driving PMOS 120 (used as a passing element), a feedback circuit 130, and a load capacitor 140. The error amplifier 110 is coupled to a reference voltage source for receiving a reference voltage VREF to compare the reference voltage VREF with a feedback voltage VFB, and the reference voltage source can be a bandgap voltage reference source. As shown in FIG. 1, the voltage level of the feedback voltage VFB is proportional to the voltage level of the output voltage VOUT with reference to the respective resistive values of the plurality of resistors which make up the feedback circuit 130. In FIG. 1, the feedback circuit 130 is constructed by a first resistor R1 and a second resistor R2. The error amplifier 110 magnifies the voltage difference between the reference voltage VREF and the feedback voltage VFB and controls the driving PMOS 120 to output the output voltage VOUT.
Therefore, conventionally, for ensure the output stability; a load capacitor 140 is required to compensate the voltage drop at the output node 150. However, due to its large size, the load capacitor 140 exorbitantly increases the required circuitry area and costs.
A new low dropout regulator is therefore desired to promote stability whilst giving consideration to the area and cost issue.